Continuous reactors of frontal polymerization in flow for the synthesis of polyacrylamide hydrogels with prescribed properties

Taking into account the fact that since the 1970s frontal polymerization (FP) reactors in flow have been the subject of our study, the work gives a brief chronology of the development of FP reactors for the synthesis of high molecular polymers, polymeric hydrogels with cross-linked structure, their advantages and drawbacks. The reasons for the impossibility of the practical implementation of tubular FP reactors in flow for the synthesis of polymers are established. The possibility of implementation of tubular FP reactors for the synthesis of polyacrylamide hydrogels (PAH) capable of absorbing and releasing large amount of water is presented. The paper also presents some data on the methods for the synthesis of PAHs with prescribed properties in tubular continuous FP reactors by way of using nano-additives and regulating the kinetics of the synthesis process. As a result, the synthesis process of PAHs with the required properties both in the absorption and release of water, and in the physical-mechanical properties was carried out in frontal tubular-type reactors in flow, and the water absorption kinetic curves and physical-mechanical properties of the obtained hydrogels are presented.

An Innovative Procedure to Evaluate the Hydrogen Diffusion Coefficient in Metals from Absorption Measurements

A large number of metallic alloys are currently under investigation in the field of hydrogen storage and hydrogen separation membranes. For such applications, the knowledge of the hydrogen diffusion coefficient in the given alloy is of great importance even if its direct measurement is not always easy to perform. In this view, the aim of this work is to describe an innovative procedure able to provide the lower limit of the hydrogen diffusion coefficient by performing hydrogen absorption kinetic experiments. Two different tools are presented: The first is a numerical code which solves the diffusion problem inside metals according to the general theory of the transport phenomena, and the second is a dimensional analysis that describes the dependence of the hydrogen diffusion coefficient from a few governing parameters. Starting from the results of several hydrogen absorption kinetic experiments performed on a Pd–Ag sample under different experimental conditions, the hydrogen diffusion coefficients were assessed by using both the described tools. A good agreement among the results obtained by means of the two procedures was observed.

Efficient Absorption of Antibiotic from Aqueous Solutions over MnO2@SA/Mn Beads and Their In Situ Regeneration by Heterogeneous Fenton-Like Reaction

Alginate has been extensively used as absorbents due to its excellent properties. However, the practical application of pure alginate has been restricted since the saturated adsorbent has weak physical structure and could not be regenerated easily. In this study, a low-cost and renewable composite MnO2@alginate/Mn adsorbent has been prepared facilely for the absorptive removal of antibiotic wastewater. FE-SEM, FTIR, and XRD analyses were used to characterize the samples. The norfloxacin (NOR) was used as an index of antibiotics. More specifically, the batch absorption efficiency of the adsorbents was evaluated by pH, contact time with different NOR concentration, and the temperature. Thus, the performance of absorption kinetic dynamics and isotherm equations were estimated for the adsorptive removal process. Parameters includingΔG0,ΔH0, andΔS0were utilized to describe the feasible adsorption process. To regenerate the saturated absorptive sites of the adsorbent, the heterogeneous Fenton-like reactions were trigged by introduction of H2O2. The results showed that the in situ regenerating has exhibited an excellent recycling stability. The high activity and the simple fabrication of the adsorbents make them attractive for the treatment of wastewater containing refractory organic compound and also provide fundamental basis and technology for further practical application.

Absorption and decomposition of ozone in a three-phase split-rectangular airlift reactor under ultrasonic irradiation

Ozone absorption was investigated in a three-phase split-rectangular airlift reactor under ultrasonic irradiation using γ-Al2O3 as catalyst. The reactor consisted of a square column (50 × 50 mm) with the height of 120 mm, divided into a riser and a downcomer by a baffle, 50 mm in width, 4 mm in thickness and 50 mm in total height. An absorption kinetic model was proposed to determine the volumetric mass transfer coefficient of ozone kLaA. The results showed that kLaA increased from 0.409 to 0.712 min−1 as power density rose from 27.2 to 100.3 W L−1, comparing with 0.242 min−1 in the absence of ultrasonic irradiation. The increase in gas flow rate and catalyst loading also favored the increase of kLaA. The degassing effect due to ultrasonic irradiation could be ignored in the ozone absorption process.